The invention relates to a reflow soldering method and apparatus wherein a shield case is employed to enclose all ventilators and the drive parts thereof for circulating a heated inert gas such as a nitrogen gas to solder base boards having electronic elements located thereon so as to prevent ambient or outside air from coming into preliminary heating chambers and inert gas chambers in which the base boards are soldered, to thereby maintain a high purity of the inert gas for the purpose of attaining a desired soldering effects.
According to the conventional reflow soldering method and apparatus using an inert gas such as a nitrogen gas, which is heated and circulated in the inert gas chambers in which the base boards are soldered, outside or ambient air is easily enters the inert gas chambers through the drive parts, that is, through the clearances between the rotational shafts of motors and the bearings thereof and/or the clearances between the drive shafts of the ventilators and lowers the purity of the inert gas in the chambers. As a result, the cream solder is oxidized and a desired soldering effect can not be attained. In order to maintain the purity of the inert gas, it is required to continuously supply the inert gas from a gas tank. This is uneconomical indeed.
For the purpose of eliminating such defects, the inventor of the present invention disclosed an invention in Japanese patent application 1-141479, an arrangement wherein the bearing parts of the ventilators are enclosed by a chamber pressurized with the inert gas. The chamber is however depressurized as the inert gas is absorbed by the ventilators and therefore a considerable amount of inert gas is uneconomically consumed.
Further, the same inventor disclosed another invention in Japanese patent application 1-202238, wherein the bearing parts of the ventilators are each enclosed and the enclosures are in communication with a high pressure part of an inert gas chamber to pressurize the enclosures so that the outside air will not come into the enclosures. This has succeeded to some degree in reducing the uneconomical consumption of inert gas, but not completely succeeded in preventing the inert gas from leaking out of the enclosures.
It is therefore a primary object of the invention to eliminate the defects and disadvantages of the prior art and to provide a reflow soldering method and the apparatus, wherein a shield case is provided to enclose ventilators for circulating an inert gas in inert gas chambers, motors for driving the ventilators and having rotational shafts operatively connected to the ventilators and refrigerators for cooling down the inert gas, to thereby prevent the motors from overheating and further prevent outside orambient air from entering the inert gas chambers, thus to maintain the purity of the inert gas to attain a desired soldering effects. It is another object of the invention to circulate the inert gas through the refrigerators to repeatedly cool the same to thereby reduce the uneconomical consumption of inert gas and further to reduce the running cost of the apparatus. It is another object of the invention to cool down a soldered base board by the cooled inert gas to prevent the metal parts of the base board from being oxidized. It is still another object of the invention to reduce the noises of the motors by enclosing the same with the shield case.